2026 South Carolina IRP

20

26

IRP

Dominion Energy South Carolina, Inc. Integrated Resource Plan

March 31, 2026

Modeling and Methodology 5

Results of the Modeling and Resource Additions 6

under the 2026 Preferred Plan

The South Carolina Energy Security Act - 7

Act 41 of 2025

Canadys Station 8

Wateree and Williams Replacements 8

The Twenty-Six Cases 9

The Core Analysis 11

Scoring the Core Build Plans on Cost 12

and CO2 Emissions Reduction

Scoring the Core Build Plans on Rate Impacts 12

Scoring the Core Build Plans on Technologies Selected 12

Scoring the Core Build Plans on Generation Diversity 12

Scoring the Core Build Plans on Reliability 12

Canadys Station and Long-Term Generation Needs 16

The Fueling Strategy for Canadys Station 18

Electric Transmission Planning 19

Canadys Station as a Potential Replacement 19

for Wateree and Williams

Peaking Generation Replacements 20

Federal Legislative Developments 21

Status of GHG Rules and Impact 22

on Modeling Requirements

ELG Compliance 22

The 2026 DSM Refresh 22

The 2026 Electrification Study 23

The 2026 Reserve Margin Study and Effective Load 23

Carrying Capability Determination

Stakeholder Process Update 24

Outages and Reliability 26

Storms and Storm Response 27

Transmission Plans and Planning 27

Transmission Projects 31

DESC's Current Generation 32

Solar and Other Renewable Generation 34

Nuclear Operating Report Update 34

Update of the Combined Cycle Generating Plants 34

Operating Report

Update of the Simple Cycle Combustion Turbines 35

Operating Report

Fossil-Steam Units Operating Report 35

Hydroelectric-Power Operating Report 35

Load Growth Forecast 36

Analysis of Load Growth Rates under 37

Alternative Economic Scenarios

Wholesale Sales 39

DSM Assumptions 39

The Percentage of Renewable Resources 42

Selected in Core Build Plans

MWs Added by the Core Build Plans 42

Natural Gas Resources Added by the Core Build Plans 42

The Specific Resources Added 43

under Each Core Build Plan

The 2026 Reference Build Plan 43

The High Fossil Fuel Prices Build Plan 44

The Medium Carbon Cost Build Plan 45

The Core Analysis 46

Levelized Cost 46

CO2 Emissions 47

Clean Energy 48

Fuel Cost Resiliency 48

Generation Diversity 49

Reliability Analysis 49

Mini-Max Regret 50

Cost Range Analysis 51

Core Build Plans Ranked Across All Metrics 51

The Near-Term Load Growth Build Plan 52

and Market Scenario

The Energy Conservation Build Plan and Market Scenario 54

The Aggressive Regulation Build Plan and Market Scenario 55

The DSM Build Plans 57

Alternative Core Build Plans

The Specific Resources Added under 63

Each Alternative Core Build Plan

The GHG Reference Build Plan 64

The GHG High Fossil Fuel Prices Build Plan 65

The GHG Medium Carbon Cost Build Plan 66

The Alternative Core Build Plan Analysis 67

Levelized Cost 67

CO2 Emissions 68

Fuel Cost Resiliency 69

Mini-Max Regret 69

Cost Range Analysis 70

Canadys Station and Near-Term Coal Unit Operation 78

Peaking Modernization Program 78

The 2023 DSM Potential Study and 2026 DSM Refresh 79

AMI Education and Residential 79

Demand Response Program

Continue the IRP Stakeholder Advisory Group Process 79

Dominion Energy South Carolina, Inc. ("DESC" or the "Company") is a vertically integrated utility that operates generation, transmission, and distribution systems that serve approximately 820,000 electric customers

and 500,000 natural gas customers in South Carolina. The Company's mission is to provide its customers and their families with reliable, affordable and increasingly clean energy to power their homes and businesses every

day. DESC has a proven record of succeeding at this mission, providing customers with uninterrupted power more than 99.99% of the

time, maintaining an impressive storm recovery record, and earning excellent safety results.

This report (the "2026 IRP") is the third comprehensive integrated resource plan ("IRP") that DESC has filed with the Public Service Commission of South Carolina (the "Commission") under the IRP Statute as revised in 2019 (the "IRP Statute").1 It requires utilities to prepare and submit a comprehensive IRP every three years.

In 2026, DESC finds itself at a critical juncture in implementing its plan to meet the future electricity needs of its customers while supporting the remarkable level of economic and population growth that the state is experiencing. Today,

South Carolina is among the fastest growing states in the nation, and DESC's electric demand is forecasted to increase 25% by 2044. This represents a 1.4% compound annual growth

rate ("CAGR") over the 25-year planning horizon, which is approximately 50% higher than the growth rate forecasted in the 2023 IRPg. DESC, as a regulated electric utility, has an

obligation to reliably serve all customers who request service within its service territory. This means that the Company must have sufficient resources and reserves to be able to instantaneously respond to hourly, daily, and seasonal spikes in customer demand against the backdrop of a steadily growing energy need in the Company's service territory.

Serving this demand and creating the ability to retire older generating units will require an "all of the above" approach that includes investment in a diverse mix of energy sources.

Against this backdrop, the General Assembly of South Carolina adopted the Energy Security Act of 2025 ("Act 41"), which recognizes the state's critical need for new energy supplies, streamlines the permitting of energy infrastructure projects and allows the South Carolina Public Service Authority ("Santee Cooper") to partner with DESC to construct a 2,180 MW advanced class combined cycle generation station in Canadys, South Carolina (the "Canadys Station"). When completed, Canadys Station is expected to be the most fuel efficient and lowest emitting natural gas facility on both utilities' systems. DESC has signed agreements to reserve major equipment and to provide natural gas transmission capacity for the project, and Canadys Station is now a committed resource for generation planning purposes.

As the IRP Statute requires, DESC has renewed its comprehensive IRP to reflect updated forecasts and multiple market scenarios. The strategies and options evaluated in the 2026 IRP support DESC's continued ability to provide safe, reliable, affordable and increasingly clean electricity to its South Carolina customers.

1 Section 58-37-40(A)

In preparing this 2026 IRP, DESC created and evaluated a total of fourteen build plans and has measured them against multiple forecasts of future customer demand, fuel costs, CO2 costs and limitations, and potential coal plant retirement scenarios. The 2026 IRP incorporates findings from new or

refreshed evaluations prepared by outside experts concerning demand side management ("DSM") potential, the reserve margin required to reliably serve customers, the effective load carrying capability ("ELCC") for solar and battery

electric storage system resources ("BESS"), and the potential contribution to customer demands from electric vehicles ("EVs") and building electrification. The 2026 IRP's analysis focuses on three Core Build Plans, the 2026 Reference Build Plan, the High Fossil Fuel Prices Build Plan, and the Medium Carbon Cost Build Plans, modeled under three Core Market Scenarios, the Reference Market Scenario, the High Fossil Fuel Prices Market Scenario, and the Medium Carbon Cost Market Scenario, each of which represents a reasonably likely forecast of future conditions.

While DESC was performing the modeling for this 2026 IRP, the United States Environmental Protection Agency ("USEPA") was completing the final steps in its review of proposed changes to the rules that it issued in 2024 under Section 111 of the Clean Air Act concerning CO2 emissions from fossil fuel-fired power stations (the "GHG Rules"). On June 17, 2025, USEPA published a proposed rule that would repeal all GHG emissions standards for fossil fuel-fired power stations. In addition, USEPA included an alternative proposal to repeal specific portions of the GHG Rules, and to revise the best system of emission reduction ("BSER") for existing coal-fired steam generating units and new base load combustion units. The proposal eliminates Carbon Capture Sequestration ("CCS") as a BSER for these units, and all CCS standards from the 2024 rules. In addition, on February 18, 2026, USEPA published a final rule rescinding

its earlier endangerment finding under the Clean Air Act which served as the legal foundation for the GHG Rules and other carbon reduction mandates under the Clean Air Act. The three Core Build Plans assume that USEPA will rescind the GHG Rules in 2026 as USEPA has indicated.

DESC has also modeled three alternative core build plans to assess its generation strategy if the current GHG Rules were to be retained or reimposed in the future (the "Alternative Core Build Plans"). DESC evaluated the three Core Build Plans and the three Alternative Core Build Plans under the three Core Market Scenarios, resulting in nine core and nine alternative cases (the "Core Cases" and the "Alternative Core Cases").

More details about the withdrawal of the GHG Rules is discussed below in "Status of GHG Rules and Impact on Modeling Requirement."

The Core Build Plans assume that DESC retires its remaining coal-only units at Wateree Station and Arthur M. Williams Station ("Wateree" and "Williams") by December 31, 2034, while the Alternative Core Build Plans assume retirement

of these units by December 31, 2032. The GHG Rules would require DESC to retire these units by December 31, 2031, but considering the lack of available short term supply alternatives, in the Alternative Core Cases DESC instructed the model

to assume that the retirement dates for these units can be delayed by one year to match the commercial operation date of Canadys Station. Should the GHG Rules remain in effect, DESC would work with regulators, policymakers, and other utilities in the state to develop an approach to continue running these units for an additional year to ensure reliable service

to customers. As noted in previous IRPs and IRP updates, the ability of the Company to retire these units depends on sufficient replacement generation being in place to meet customers' current and forecasted demands at the time that the retirement decisions are made.

In addition to the Core and Alternative Build Plans, DESC developed five other build plans as sensitivity cases (the "Sensitivity Cases") to assess how generation planning might vary under alternative market scenarios and to satisfy specific statutory and regulatory requirements. The five Sensitivity Cases are the Near-Term Load Growth Build Plan, the Energy Conservation Build Plan, the Aggressive Regulation Build Plan, the High DSM Build Plan, and the Low DSM Build Plan.

DESC also modeled three supplemental cases (the "Supplemental Cases") resulting in three supplemental build plans (the "Supplemental Build Plans"). They are the Optimized Retirements - Reference Build Plan, the Optimized Retirements - High Load Build Plan and the Deep Decarbonization Build Plan. DESC prepared the first two Supplemental Build Plans

as requested by ORS and adopted by the Commission to perform an optimal retirement analysis of the Wateree and Williams units.2 The Optimized Retirements - Reference Build Plan is based on the reference load growth forecast and retires Wateree on December 31, 2032, and Williams on December

31, 2046. The Optimized Retirements - High Load Build Plan is based on the high load growth forecast and retires Wateree on December 31, 2044, and Williams on December 31, 2046. The third Supplemental Build Plan, the Deep Decarbonization Build Plan, evaluates a build plan to reduce DESC's CO2 emissions

from its 2005 baseline by 85%. It requires extensive and costly

investment in renewables, storage, and nuclear resources to manage intermittency and support system reliability.

The modeling performed for this 2026 IRP shows that the 2026 Reference Build Plan is the preferred build plan which reflects the most likely market scenario and is resilient under the twenty-six Core, Alternative, Sensitivity and Supplemental Cases. Furthermore, in the initial years of the study period the generation resources added under the 2026 Reference Build Plan are sufficiently comparable to those that would be added under the other thirteen build plans to allow DESC to pivot to an alternative plan at any time during which this 2026 IRP is in effect.

As shown in Figure 1, the 2026 Reference Build Plan builds a total of 5,344 MW of new generating resources over the planning horizon of which 2,400 MW are new photovoltaic solar generation ("Solar"), 300 MW are new battery energy

storage ("Battery"), and 600 MW are new solar with associated battery storage ("Hybrid Solar & Storage"). The 2026 Reference Build Plan replaces Wateree on December 31, 2032, and Williams on December 31, 2034, with Canadys Station and Hybrid Solar & Storage resources. Additionally, to ensure reliability and affordability, the 2026 Reference Build Plan adds a 466 MW advanced class frame combustion turbine ("Frame CT") in 2040 and two large Frame CTs totaling 480 MW in 2045.

1. The requirements were suggested by the South Carolina Office of Regulatory Staff and included by the Commission in Order No. 2025-660.

   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   

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   Figure 1. Resource Additions under the Preferred Plan - the 2026 Reference Build Plan

   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   

   The GHG Reference Build Plan adds 5,300 MW of new Solar, 1,400 MW of new Battery, 600 MW of new Hybrid Solar & Storage, and 1,500 MW of Offshore Wind ("OSW") to meet customer demands with the GHG Rules in place. The model selects OSW to come on-line in 2049 and 2050. The 2026 Reference Build Plan and GHG Reference Build Plan build similar resources with the main divergence being that the GHG Reference Build Plan builds significantly more resources in total (9,898 MW compared to 5,344 MW) largely by adding Solar and Battery capacity and OSW with additional gas resources needed to support reliability. However, the GHG Reference Build Plan does not build the three Frame CTs modeled in the 2026 Reference Build Plan.

   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   

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   Figure 2. Resource Additions under the GHG Reference Build Plan

   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   

   The Supplemental Build Plans show that in a high load growth environment delaying the retirement of Wateree and Williams to dates as late as December 31, 2044, and December 31, 2046, respectively, could be economically feasible; however, the 2026 Reference Build Plan and the GHG Reference Build Plan retire both plants by 2034.

   These 2044 and 2046 retirement date assumptions are based on DESC's currently approved depreciation study which identified those dates as the end of the economically useful lives of those units. As stated in multiple prior IRPs and IRP updates, in all cases the retirement of these units depends on DESC having sufficient generation to serve actual and forecasted load at the time that the decision is made to retire

   them. DESC will continue to evaluate the appropriate date for retiring these units as conditions on its electric system evolve.

   Based on these modeling results, and a careful review of the current needs of the electric system, DESC has selected the 2026 Reference Build Plan as its preferred plan to guide its planning decisions at the present time.

   The South Carolina Energy Security Act -Act 41 of 2025

   Last year, the South Carolina General Assembly passed Act 41 with bipartisan supermajorities in both chambers. It did so in response to warnings from the South Carolina

   Department of Commerce, ORS and others that absent new electric generation, the reliability of the electric grid and the State's ability to sustain economic development would be compromised. Act 41 states the legislative finding that "[g]iven the importance of sufficient, reliable, safe, and economical energy to the health, safety, and well-being of the citizens of South Carolina and to the state's economic development and prosperity…the prompt siting, permitting, and completion of energy infrastructure projects, energy corridor projects, and brownfield electrical generation projects are crucial to the welfare of the State."

   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   

   In Act 41, the General Assembly authorized Santee Cooper to jointly own "one or more natural gas-fired generation

   facilities, and related transmission facilities, to be constructed on a site at or near Dominion Energy South Carolina, Inc.'s former Canadys coal-fired generation station in Colleton County." S.C. Code Ann. § 58-31-205(A). The Canadys site is located approximately forty miles north of Charleston, South Carolina, and was home to three coal fired units, the last of which was retired in late 2013. Act 41 encourages DESC and Santee Cooper to complete their evaluation of the project, which is both an energy infrastructure and brownfield electric generation project under the terms of Act 41.

   Canadys Station

   On December 15, 2025, DESC and Santee Cooper filed a Joint Application for a Certificate of Environmental Compatibility and Public Convenience and Necessity for Canadys Station under

   S.C. Code Ann. § 58-33-110, the Siting Act. The application is currently under review in Docket No. 2025-323-E with a final order expected in June 2026. More details about Canadys Station are discussed below in "Canadys Station Update."

   Electric transmission system upgrades to deliver power from Canadys Station to DESC and Santee Cooper's respective systems' customers will be the subject of future Siting Act filings. The scope of the upgrades required on the DESC system is well understood based on prior Transmission Impact Analyses ("TIAs") and general knowledge of transmission operating constraints in the Charleston area. The majority of the upgrades for Canadys Station will involve modernizing existing electric transmission assets including older wood frame circuits in the Lowcountry that DESC will replace with modern, reliable, storm resilient steel monopoles and high-capacity bundled conductors.

   Wateree and Williams Replacements

   DESC's current plan is to retire Wateree during 2032 and Williams during 2034 following the commercial availability of Canadys Station.3 Williams represents approximately 80% of DESC's generating capacity in the Charleston area and the retirement of Williams will only be possible when Canadys Station is in service along with the transmission facilities needed to ensure reliability is maintained in the greater

   Charleston area. From an engineering standpoint, Wateree and Williams can continue to provide generating capacity until the end of their useful lives which are currently forecasted to occur in the mid-2040s. Two of the Supplemental Build Plans have optimized the retirement of both units based on their current

2. The accepted convention in generation planning is that an addition or retirement of a generating unit is recognized in the year following the event. Therefore, a retirement taking place in 2032 would be recognized in 2033.

   forecasted end of useful life. However, DESC's current plan retires both facilities before that time.

   
   
   

   Canadys Station Site; Colleton County, SC

   
   
   

   Wateree Station; Richland County, SC

   
   
   

   Williams Station; Goose Creek, SC

   In its 2026 IRP, DESC has evaluated a total of fourteen build plans, each of which reflects a unique balance of affordability, generation diversity, carbon emissions reductions, and environmental compliance assumptions. Collectively the fourteen build plans represent a broad range of available options to serve DESC's approximately 820,000 electric customers in South Carolina safely, reliably, and cost effectively under a diverse set of potential future market conditions and approaches to carbon reduction. All fourteen Build Plans envision an "all of the above" strategy which includes the expansion of Solar, Battery, and Hybrid Solar & Storage, while adding the dispatchable and non-energy limited generation resources needed to ensure that the reliability of the grid is protected. DESC has analyzed the fourteen Build Plans across twenty-six individual cases to evaluate how

   well each performs under a range of different assumptions

   concerning fuel costs, environmental costs and restrictions, customer loads, and other market conditions.

   The Twenty-Six Cases

   DESC modeled the three Core and three Alternative Core Build Plans across the three most likely Market Scenarios, resulting in nine Core and nine Alternative Core Cases. The

   five Sensitivity Cases assess how build plans might vary under alternative market conditions and satisfy specific statutory

   and regulatory requirements. Two of the three Supplemental Cases evaluate the optimum retirement dates for Wateree and Williams under medium and high load forecasts. The third Supplemental Case assesses the types and levels of resources required for DESC to achieve a reduction in CO2 emissions of

   85% from a 2005 baseline by 2050.

   Table 1: The 8 Market Scenarios, 14 Build Plans, and 26 Cases

   Market Scenarios (8)	Build Plans (14)	Cases (26)
   Core Cases
   Reference	2026 Reference Build Plan	Three Core Build Plans combined with Three Market Scenarios = 9 Core Cases	9
   High Fossil Fuel Prices	High Fossil Fuel Prices Build Plan
   Medium Carbon Cost	Medium Carbon Cost Build Plan
   Sensitivity Cases
   Near-Term Load Growth	Near-Term Load Growth Build Plan	Five Sensitivity Cases	5
   Energy Conservation	Energy Conservation Build Plan
   Aggressive Regulation	Aggressive Regulation Build Plan
   Low DSM	High DSM Build Plan
   High DSM	Low DSM Build Plan
   Supplemental Cases
   Reference	Optimized Retirements - Reference Build Plan	Three Supplemental Cases	3
   High Load	Optimized Retirements - High Load Build Plan
   Reference	Deep Decarbonization Build Plan
   Alternative Core Cases
   Reference	GHG Reference Build Plan	Three Alternative Core Build Plans combined with Three Market Scenarios = 9 Alternative Core Cases	9
   High Fossil Fuel Prices	GHG High Fossil Fuel Prices Build Plan
   Medium Carbon Cost	GHG Medium Carbon Cost Build Plan
   		TOTAL	26

   Overview of the Build Plans, Market Scenarios, and Cases

Each of the three Core Build Plans is optimized to achieve the lowest cost for customers across different market conditions and assumptions, while protecting reliability and supporting CO2 emissions reductions. The Core Cases show how those plans respond under a broad range of conditions.

• The 2026 Reference Build Plan is optimized under the most reasonable and likely future market conditions.

• The High Fossil Fuel Prices Build Plan assumes

  high fossil fuel costs in an environment where public policy discourages investment in fossil fuels production and delivery systems, and through the

  resulting increases in fossil fuel prices, achieves policy objectives without the need to impose separate

  CO2 costs.

• The Medium Carbon Cost Build Plan assumes policies towards fossil fuels are neutral or favorable resulting in moderate fuel costs and medium CO2 costs.

Table 2 presents twenty-six cases, with the nine Core Cases in blue, the five Sensitivity Cases in orange, the three Supplemental Cases in green, and the nine Alternative Core Cases in grey.

Table 2: The Twenty-Six Cases

The Core Analysis compared the results of the three Core Build Plans across the three Core Market Scenarios for a total of nine Core Cases. The three Core Build Plans and three

Core Market Scenarios are all based on the Reference load projection so that all results show the costs and CO2 emissions from meeting the same level of customer demand and

therefore can be compared on a comparable basis.

The Company also conducted a similar analysis of the relative performance of the three Alternative Core Build Plans against the Core Market Scenarios to gauge their relative performance in an environment involving regulations comparable to the 2024 GHG Rules.

Table 3: The Nine Core Cases

The 2026 Reference Build Plan had the lowest cost to customers expressed as the levelized net present value ("LNPV") cost per year for generation supply across all nine Core Cases. The 2026 Reference Build Plan has a materially lower cost than the two other Core Build Plans, specifically the High Fossil Fuel Prices Build Plan and the Medium Carbon Cost Build Plan. The differences in cost between the latter two build plans were relatively small, between 0.7% and 2.2%.

The High Fossil Fuel Prices Build Plan had the highest LNPV cost across all three Core Market Scenarios, with an annual LNPV cost between $20 million and $121 million more than the lowest cost plan under each Market Scenario. The difference between the 2026 Reference Build Plan and the High Fossil Fuel Prices Build Plan for each Market Scenario was difference in costs to customers between -0.1% and 5.1%.

The Core Build Plans resulted in DESC reducing its CO2 emissions between 58.3% and 70.0% compared to emissions in 2005. The High Fossil Fuel Prices Build Plan achieved the greatest CO2 emissions reduction of the Core Build Plans producing a 70.0% reduction in CO2 emissions from 2005 levels. CO2 emissions reductions among the remaining two Core Build Plans vary between 58.3% and 68.4%, with the 2026 Reference Build Plan having the lowest reduction of 58.3%.

The 2026 Reference Build Plan has the lowest CAGR for a typical residential customer's bill (i.e., typical 1,000 kWh/month usage) over a 15-year period planning horizon under all three Core Market Scenarios with a CAGR between 3.33% and 4.26%. The Medium Carbon Build Plan is second lowest in all Market Scenarios, with a CAGR between 3.60% and 4.31%. The High Fuel Build Plan has the highest CAGR in all Market Scenarios with annual growth in a typical residential customer's bill between 3.71% and 4.35%. The residential customers' CAGR scoring differs from the system's LNPV score because the difference in usage patterns and rate designs between residential customers and other customer classes results in a different allocation of costs between residential customers and the system generally.

These CAGR figures represent only the change in customers' bills under the three Core Build Plans due to forecasted changes in generation supply costs and the application of

general inflation indices to other cost categories. They are provided as a comparative measure for the build plans and not as a comprehensive forecast of future customer rates.

Solar, Battery, and Hybrid Solar & Storage emerged as major contributors in each of the Core Build Plans with

renewable generation from Solar and Hybrid Solar & Storage representing between 56% and 73% (3,000 MW and 6,800 MW) of the resources added (on a nameplate basis) and storage from Battery and Hybrid Solar & Storage representing between 16% and 18% (900 MW and 1,500 MW) of those resources.

While each of the Core Build Plans adds at least 62% of non-emitting resources (on a nameplate basis), each also adds at least 1,578 MW of natural gas-fired generation to support

system reliability, demonstrating that dispatchable, non-energy limited generation remains critically important to grid reliability and generation efficiency.

All Core Build Plans envision that Solar will account for at least 56% of generation added over the planning horizon from both Solar and Hybrid Solar & Storage, and all Core Build Plans include the eventual elimination of coal as a fuel for electric generation. Because the build plans strongly favor Solar, generation diversity is inversely proportional to the Solar resources added. Of the Core Build Plans, the 2026 Reference Build Plan had the greatest generation diversity, the Medium Carbon Build Plan was second, and the High Fossil Fuel Prices Build Plan was third.

The reliability metric measures the diversity of generation sources added by the individual build plans. Among the Core Build Plans, the High Fossil Fuel Prices Build Plan and the Medium Carbon Build Plan scored highest under the reliability metric principally due to the relatively high amount of Battery and natural gas capacity added to the system under those plans, which contributed to the high cost of that build plan. The 2026 Reference Build Plan scored approximately the same as the other two Core Build Plans, within 7%.

In addition to the Core Analysis, DESC modeled five Sensitivity Cases to evaluate the potential effects on DESC's generation plans of changes in fuel cost, CO2 costs, load growth, and DSM effectiveness. DESC also modeled three Supplemental Cases to optimize the retirements of Wateree and Williams under different load forecast conditions, and to assess the types and levels of resources, based on the Reference Market Scenario, to achieve a reduction in CO2 emissions of 85% by 2050 to be accomplished in stages beginning in

2031. These eight Non-Core Build Plans confirm the representative nature of the Core Build Plans and the value of the planning insights they provided.

DESC presents the detailed composition and scoring of the build plans beginning with "The Core Build Plan Analysis."

Table 4: The Non-Core Build Plans

In evaluating resource plans, the IRP Statute requires the Commission to consider whether the IRP balances multiple factors, including resource adequacy, least cost to customers, environmental compliance, reliability, exposure to commodity price risk, and diversity of generation and fuel supply. DESC's 2026 IRP presents build plans showing how this balance can be achieved and provides a sound basis for the Company to plan for providing safe, reliable, affordable, and increasingly clean energy to its customers

in future years. Appendix K cross-references the sections of this 2026 IRP to the requirements of the IRP Statute and other regulatory requirements.

IRPs are snapshots in time based on current forecasts of customers' future energy needs, future environmental constraints, future fuel prices and availability, and the cost or availability of rapidly evolving generation resources and technologies. The modeling done in IRPs is based on assumed costs and configurations of available generation technologies, in most cases without information concerning project or location-specific costs or site-specific transmission system upgrade costs. Accordingly, an IRP provides a critically important roadmap and framework for monitoring and assessing the impacts of changes in customer demands, environmental policies, fuel, and technology costs to inform future decision making. The IRP and IRP updates do not supplant the Commission's role in reviewing applications under the Siting Act for authorization to proceed to build a specific project, and committed resources aside, nothing in this 2026 IRP reflects a fixed decision by DESC to pursue any specific action or project.

Based on this 2026 IRP, DESC will continue to analyze and define the most reasonable path for it to add increasingly clean generation resources as it pursues the modernization of its generation fleet and the eventual retirement and replacement Wateree and Williams, all while meeting customers' energy needs safely, reliably and affordably, today and in the future. DESC will continue to meet with the South Carolina Office of Regulatory Staff ("ORS") and IRP stakeholders ("Stakeholders") on a regular basis to receive comments on the methodology and inputs used in future IRPs and IRP updates. DESC has carefully reviewed and considered the comments and suggestions received on this 2026 IRP and will continue to do so in the future.

Resource planning is conducted throughout the year by the Company for multiple planning and resource procurement purposes. When future procurement or retirement decisions are considered, DESC updates its resource plans to reflect current needs and conditions on its system and in the industry. Given the pace of change in environmental policies, generation technologies, and the expectations of customers and other stakeholders, it is important that the Company remains flexible with respect to build plans and the asset procurements and retirements they reflect. The fact that DESC modeled the selection or retirement of any resource in

this 2026 IRP does not mean that DESC has made the decision to procure or retire any such resource or that such a decision has been approved by the Commission where such approval is required. DESC will present these decisions to the Commission as appropriate at the time they are made or proposed, in accordance with the Siting Act and other regulatory requirements.

For nearly two decades, DESC has been steadily reducing the environmental impacts and air emissions from its electric generation fleet by retiring or repowering coal plants, integrating third-party owned and operated solar, and adding modern, high-efficiency natural gas generation while remaining focused on reliability and affordability for its customers. Since 2000, DESC has either retired or converted eight coal units to natural gas operation, and from 2005 through 2024, carbon emissions have fallen by approximately 44% despite robust growth in energy consumption on its system.

Figure 3: DESC's Historical Annual CO2 Emissions 2005-2024 MT

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2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024

DESC's selection of the 2026 Reference Build Plan as its preferred plan to guide its planning decisions at the present time is consistent with its commitment to reducing carbon emissions. The preferred plan adds significant renewables and storage related resources including Solar, Battery and Hybrid Solar & Storage, while also pursuing the eventual retirement of Wateree and Williams by investing in modern, efficient generating capacity that can assist in those retirements. As market dynamics, public policy and technologies evolve, DESC will continue to evaluate plans reflecting further carbon reductions consistent with DESC's mission of providing its customers with reliable, affordable, and increasingly clean energy.

Canadys Station Combined Cycle Conceptual Rendering

Since 2020, the Company's triennial IRPs and annual IRP updates have consistently identified the need for new, efficient natural gas-fired generation to support its customers' longterm generation needs. While as would be expected, the

exact size and configuration of the natural gas resources have varied across IRPs and annual IRP updates, each analysis has shown that a single project consisting of several hundred megawatts of new natural gas generation is necessary to reliably serve customer load, sustain economic development, and support the Company's planning reserve margin. Growing customer demand in the South Carolina Lowcountry (the greater Charleston metropolitan region along with Jasper, Beaufort, and Colleton counties), coupled with the potential future retirement of Wateree and Williams presents a challenge in ensuring that there are sufficient generating resources to reliably serve the Company's customers and to meet their existing and future energy needs.

The 2023 IRP selected a new combined cycle plant as the next major increment of capacity in all build plans. The resource identified at that time was either a 50% ownership share of a combined cycle plant providing DESC with 662 MW of new capacity, or under certain market scenarios, a 100% share

of a 1,325 MW combined cycle plant. The 2024 IRP Update determined that a large combined cycle resource in either the

662 MW or 1,325 MW configuration was the optimal resource to add under a broad range of market scenarios including

the two most highly carbon-constrained scenarios4 and the scenario that assumed the highest future commodity cost of natural gas.5 The 2025 IRP Update assumed Canadys Station would be a larger combined cycle configuration with DESC's 50% ownership share providing 998 MW of capacity.

The combined cycle plants that DESC modeled in 2023 IRP and the 2024 and 2025 IRP Updates reflected sizes that were based on then-current information concerning the standard or most commonly available offerings of combined cycle resources. In moving forward with the Canadys Station project, DESC and Santee Cooper refined this sizing based on specific engineering data, operational considerations, pricing, and other information provided in response to requests for information from equipment suppliers and others.

Based on this information, DESC and Santee Cooper determined that the most cost effective and operationally sound configuration of Canadys Station is one consisting of three independent blocks of highly efficient and low emitting advanced class one-on-one ("1x1") combined cycle units providing approximately 2,180 MW of total capacity in winter. In this configuration, Canadys Station will provide Santee Cooper and DESC with modern, reliable, and operationally flexible generation resources to meet customers' current and future energy needs.

1. The 2024 Proposed GHG Rule Build Plan and 85% CO2 Reduction Build Plan.

2. The 2024 High Fossil Fuel Prices Build Plan.

   Canadys Station Update

Canadys Station will be an advanced class6 combined cycle natural gas facility consisting of three, independent, multi-shaft7 1x1 combined cycle generating blocks. Each 1x1 generating block will consist of one approximately 450

MW combustion turbine-generator ("CTG") paired with one approximately 280 MW steam turbine-generator ("STG"). Each STG primarily generates electricity from heat recovered from the exhaust of its associated CTG through heat recovery steam generators ("HRSG"). Canadys Station will have three CTGs, STGs and HRSGs. Each STG will exhaust its residual steam into an air-cooled condenser ("ACC"), where the steam will be cooled, condensed into water, and recirculated for reuse in the HRSG and STG steam cycle in a closed loop that limits evaporative losses and requires little makeup water. The makeup water for the plant's steam cycle, diluent injection for emissions control when the CTGs are operating on liquid fuel, and cooling water for the combustion turbine inlet chilling system will principally come from deep groundwater wells but may at times be supplemented with surface water withdrawal from the Edisto River to support conjunctive water usage.

For its primary fuel, Canadys Station will use pipeline-quality natural gas delivered to the site under long-term firm transportation ("FT") agreements with interstate natural gas pipelines subject to FERC jurisdiction. The pipeline expansion project that will connect directly to Canadys Station is an extension of the Kinder Morgan-affiliated Elba Express

Company, LLC pipeline (the "Bridge Project"). Canadys Station will also be designed with the ability to fire liquid fuel and

1. "Advanced class" refers to latest generation of large combustion turbine generator technology for units with higher power density, firing temperatures, and overall thermal efficiency (i.e., "G-", "H-" or "J-class" units depending on the manufacturer).

2. "Multi-shaft" refers to the combustion turbine-generator and steam turbine-generator each operating in a separate physical drivetrain, each with its own electrical generator.

will maintain a reserve of ultra-low sulfur fuel or heating oil, delivered by truck, and stored on site as a backup fuel in the unlikely event of a disruption in FT service. The facility will have sufficient on-site storage for approximately 72 hours of operation on fuel oil.

Canadys Station's three advanced class combustion turbines will be equipped with combustion turbine inlet chilling equipment to maximize the output of the plant during hot weather. The plant design will also incorporate supplementary firing of natural gas in the HRSGs (commonly referred to as "duct firing"). Supplementary firing equipment consists of natural gas-fired burners located in the HRSGs downstream of the CTGs. Duct firing increases the output capability from the STGs by facilitating additional steam production from the HRSGs. This provides additional year-round generating output capacity at a relatively low incremental capital cost.

The multiple 1x1 combined cycle generating block configuration maximizes operational flexibility, reliability, and resiliency and mitigates "single point" contingencies that could impact a significant amount of generation on both the DESC and Santee Cooper systems. DESC and Santee Cooper anticipate a phased approach to the commercial operation of the Canadys Station generating blocks, with the full output

of the facility entering commercial operation in 2033 but with individual 1x1 combined cycle units coming online as they are completed. In keeping with generation planning conventions, the full output of Canadys Station is assumed in the IRP model to become available on January 1, 2033, as a single new increment of capacity. As modeled in the 2026 IRP, on that date Canadys Station will begin providing DESC with approximately 1,098 MW of fully dispatchable, highly responsive, and highly efficient baseload-capable capacity that can be used to support the replacement of existing coal fired generation and to meet increasing customer demands over the ensuing decades.

The operational flexibility of three 1x1 combined cycle units will improve grid reliability at all times, especially during extreme weather while supporting the integration of increasing levels of intermittent, non-emitting, solar generation. Canadys Station will provide generation and electric transmission support for the Charleston area and will represent an important step towards the eventual retirement of Williams.

DESC will lead the overall development, construction, and eventual operation of Canadys Station with oversight and in close collaboration with Santee Cooper as its project partner. Construction of the facility will be subject to monitoring by an independent construction analyst retained by ORS under the requirements of Act 41. DESC executed an equipment reservation agreement with the selected supplier of the combustion and steam turbine-generators and heat recovery

steam generator equipment and has procured the large power transformers for the project. DESC and Santee Cooper intend to select the Engineering, Procurement and Construction ("EPC") contractor later in 2026. The in-service date for the entire Canadys Station facility is modeled for the purposes of the 2026 IRP to occur on January 1, 2033, but it is anticipated that individual 1x1 combined cycle generating blocks will come online in phases prior to completion of all three.

The focus on the Canadys site was due to multiple factors-land use considerations, proximity to load, access to water supplies, proximity to electric transmission infrastructure, and the feasibility of expanding natural gas transportation services to the site. All of these considerations are foundational when siting a natural gas-fired generation resource.

DESC and Santee Cooper have completed the joint evaluation as prescribed by Act 41 and selected the Canadys site as the best site for the project. As a brownfield site, the Canadys site is environmentally well-characterized and offers robust electric transmission interconnectivity from rights of way that radiate from the site toward major load centers including the greater Charleston area forty miles to the east. The site also sits near existing and planned Santee Cooper electric transmission lines. The site was used for large scale electric generating activities for decades. It offers robust electric transmission interconnectivity through multiple rights of way radiating out from the site, including key corridors leading toward major load centers and transmission hubs in coastal South Carolina.

Additionally, Santee Cooper has existing, near-term plans to construct a new 230 kV transmission pathway along the Interstate 95 corridor, close to the Canadys site, which will

simplify Santee Cooper's interconnection of Canadys Station into their balancing area. Further, the site is well-positioned for supporting the expansion of natural gas transportation infrastructure to supply fuel for new generation. By pursuing the project jointly, DESC and Santee Cooper are creating economies of scale in generation plant construction and

operation and natural gas pipeline and electric transmission expansion. The benefits and savings achieved through

their collaboration ultimately will flow to the customers of both utilities.

Canadys Station will also anchor a major expansion of natural gas pipeline capacity into South Carolina, which will serve the South Carolina Lowcountry where economic development

is increasingly limited by lack of access to firm natural gas transportation service. To fuel Canadys Station, DESC has executed three precedent agreements ("PAs") supporting pipeline expansion projects that will provide FT service from robust hubs of natural gas production and supply to the Canadys site. DESC is not the only customer for the two

largest of these expansion projects; it is participating in these expansion projects alongside other rapidly growing utilities in the Southeastern United States.

Fueling Canadys Station requires DESC and Santee Cooper to hold FT capacity linking the facility to commercial natural

gas trading hubs where sufficient supply is available to ensure a liquid market. DESC entered into two PAs for long-haul interstate natural gas transportation back to major trading hubs. These two PAs are for participation in the South System Expansion 4 ("SSE4") and the Mississippi Crossing ("MSX") pipeline expansion projects. DESC is not the sole customer for these projects-both SSE4 and MSX have elicited considerable interest from other shippers that have signed on to these expansion projects. DESC is participating in these projects

as an "anchor shipper" which provides important price and contractual protections. Regulatory approvals for the SSE4 and MSX expansion projects are pending at the Federal Energy Regulatory Commission ("FERC") under Section 7(c) of the Natural Gas Act.

In March of 2025, DESC executed a third and final Precedent Agreement for an expansion project to secure firm natural gas transportation from the terminus of the SSE4 expansion project near the Georgia-South Carolina border to the Canadys site. This expansion project will complete the route to Canadys while also providing access for additional firm gas transportation for other customers in South Carolina to support and sustain economic development in this region of the State. The timing and availability of additional natural gas transportation capacity to the site is subject to federal

approvals by FERC and therefore is outside of the direct control of DESC, Santee Cooper, and South Carolina policymakers.

Receiving these approvals in a timely manner is a key scheduling consideration for Canadys Station. All indications remain that sufficient additional capacity can be provided in a timely way to support construction of the facility.

While Canadys Station is the foundational customer to support this expansion of natural gas availability in South Carolina, other customers stand to benefit from this expansion including prospective and existing industrial customers looking to secure firm natural gas transportation service, and local natural gas distribution systems including DESC's local gas distribution system which will acquire 35,000 DT/day of FT on this pipeline expansion. The lack of incremental FT service on natural gas systems has become an increasingly important limitation on the economic development potential in parts of South Carolina; and Canadys Station will provide an opportunity to overcome that limitation.

In August 2024, DESC submitted interconnection requests for Canadys Station into the 2024 Definitive Interconnection System Impact Study ("DISIS") cluster study process which DESC conducts annually under its FERC-regulated Open Access Transmission Tariff ("OATT"). Through this process,

DESC's transmission planning group is identifying a definitive list of electric transmission upgrades and associated cost allocations and construction schedules required to interconnect the facility with DESC's transmission system. Future reports from the DISIS cluster study process and affected system studies conducted with Santee Cooper and other neighboring utilities will inform future filings under the Siting Act for network electric transmission upgrades associated with Canadys Station. However, the nature and scope of the required upgrades on DESC's system are well understood based on prior TIA analyses conducted to identify the upgrades necessary to connect a large combined cycle natural gas facility unit at the Canadys site to the grid, and DESC's operational knowledge of the transmission facilities in the area that are stressed or limited in times of high demand or when Williams is not online.

The TIAs prepared to date through the IRP process indicate that one of the principal schedule drivers for being able to utilize the full output of Canadys Station on a firm basis will be the time required to complete the requisite generation interconnection studies and then design, siting, procurement, and construction of the electric transmission assets needed for the replacement generation resources, particularly as other generating projects participate and withdraw in the DISIS cluster study process. This process is well underway and DESC and Santee Cooper are working in close collaboration to

ensure that the requisite electric transmission upgrade projects will be completed to support the construction and operation of the facility.

Existing Canadys 230KV/115KV Substation located on the Canadys brownfield site

When the 2023 IRP was filed, the preferred plan modeled the replacement of the 684 MW of Wateree capacity with 400 MW of Battery at the Wateree site while relying on existing capacity reserves to supply the balance of the required capacity.

Since 2023, economic development projects have added approximately 256 MW of demand to DESC's load forecast making the prior plan impractical and creating a capacity need large enough to justify coordinating the potential retirement of Wateree with the construction of the larger, more efficient and lower emitting combined cycle generating resource at Canadys. The 2026 IRP shows that completion of Canadys Station is required to maintain system reliability when DESC retires Wateree Station.

The potential future retirement of Williams Station will require DESC to add major generating resources in addition to Canadys Station, but Canadys Station's physical location and the associated electric transmission upgrades that will integrate it into the DESC system will play a key role in maintaining reliability in the Charleston area when Williams retires. The transmission system that serves the Charleston area is under increasing stress as loads in the area increase. While capacity from Canadys Station will not be sufficient to fully retire Wateree and Williams on a one-for-one basis, the facility will provide locally available capacity in the Charleston

area and regional support for the transmission system that will be of primary importance when DESC retires Williams. DESC will continue to study and evaluate the eventual retirement of Williams, along with the retirement of Wateree as conditions on its system developg.

Key developments related to DESC's generation planning include the passage of Act 41 by the South Carolina General Assembly, continued progress on the design, procurement and permitting of Canadys Station, USEPA's steps toward withdrawing the GHG Rules, recent revisions to the ELG Rules, and USEPA's on-going review of the ELG and MATS rules,

and PM2.5 regulations. The analysis of these developments is found in both "Executive Summary" above, and below.

In March 2021, DESC applied to the Commission for rulings to allow the Company to proceed with its plan to retire thirteen end-of-life and increasingly difficult to maintain natural gas-fired combustion turbine ("CT") units and one natural gas-fired steam unit. Despite their age and condition, these older units have played an important role in maintaining grid reliability by providing DESC with the ability to respond to changes in load and intermittent generation and, if needed, through black start capabilities to restart the grid after blackouts. In November 2021, the Company entered into a Partial Settlement, which allowed for the retirement and replacement of most of these units to proceed. The exception was the retirement and replacement of several units at Urquhart Station, which the Partial Settlement required to be the subject of an all-sources request for proposal (the "Urquhart RFP") for replacement capacity. The Commission approved the Partial Settlement in Order No. 2022-27.

The Hardeeville, Bushy Park, Parr, and Coit Retirements and the Bushy Park and Parr Replacements

Upon Commission approval of the Partial Settlement, DESC proceeded with the retirement of seven CT units at four sites, one unit at Hardeeville, two units at Bushy Park, and four units at Parr, and to construct three modern aeroderivative combustion turbine ("Aero CTs") units as replacements with one unit at Bushy Park and two at Parr. DESC retired the Hardeeville unit effective March 31, 2022, the Bushy Park units effective September 30, 2022, and the Parr units effective March 31, 2023. Dismantling and demolition activities were

completed at Hardeeville and Bushy Park in 2022 and at Parr in 2023. DESC subsequently retired the two Coit CT units, which it did not otherwise replace, following commercial availability of the new Parr units at the end of 2025. Dismantling and demolition activities of the Coit CT units are anticipated to be substantially completed in 2026.

The replacement Bushy Park unit ("Bushy Park CT #1") entered commercial operation on November 1, 2024, and has contributed to system operations since. Construction of the replacement Parr Station units ("Parr CT #1" and "Parr CT #2") was completed in the summer of 2025 and these units entered commercial operation on December 1, 2025.

Bushy Park CT #1 Unit (In Commercial Operation)

Parr Station CT #1 and CT #2 Units (In Commercial Operation)